1. Technical Field
The present invention relates to a film-forming apparatus and a method of forming film.
2. Related Art
Conventionally, spin coating or flexographic printing is commonly used as a method for forming a color filter or another functional thin film on a substrate. In contrast, in recent years, droplet discharging is used for forming various thin films because the method is effective for reducing ink consumption and the number of production steps. With the method for forming a thin film using the droplet discharge method, ink in which functional material (solid content) is dissolved or dispersed in a solvent (dispersion medium) is discharged onto the substrate as droplets and arranged in desired positions, whereupon the ink thus arranged is dried to remove the solvent (dispersion medium) in the ink and thereby form a thin film composed of the functional material.
Color filters, wiring, or other industrially formed functional thin films are becoming increasingly downscaled and made smaller in recent years. Therefore, higher discharge precision is required when these functional thin films are formed using the droplet discharge method. Based on this background, discharge precision has been improved in recent years by using a chamber to accommodate discharge heads for discharging droplets and controlling the discharge head environment, such as Japanese Laid-open Patent Application Nos. 2004-167431 and 2005-146768.
With a film-forming apparatus in which the discharge heads are so accommodated inside a chamber, there is variability in the ink discharge amount, ink deposition accuracy is reduced, and there are other problems in that the ink begins to dry and viscosity is increased in nozzles that do not perform a discharge operation among the plurality of nozzles provided to the nozzle surface, for example, because the nozzle surface of the discharge heads is in a state exposed to atmosphere inside the chamber.
In view of the above, with such a film-forming apparatus, maintenance processing must be carried out on a regular basis in order to maintain or restore a good discharge state for droplets discharged from the nozzles. Specific operations that are carried out include a flushing operation for discharging ink from the nozzles so that the viscosity of the ink does not increase; a suction operation for removing higher viscosity ink from inside the nozzles and removing foam from inside the cavities by mounting a cap on the nozzle surface (capping) and performing suctioning via the cap; and a wiping operation for removing deposits adhering to the nozzle surface, by wiping the nozzle surface with a wiping member. Such a maintenance process is ordinarily carried out in a maintenance area that is provided separately from the drawing area for forming a film by discharging ink (functional liquid) onto a substrate.
However, the film-forming apparatus described above has the following problems that need to be improved.
The discharge heads used in the film-forming apparatus and the control device provided with an electronic circuit for applying an electric signal (drive signal) to the discharge heads both undergo self-heating during operation. The control device is ordinarily arranged near the discharge heads. Therefore, the temperature of the discharge heads becomes greater than the ambient temperature (atmospheric temperature) due to the heat produced by the discharge heads and by the heat produced by the control device, and the temperature of the members near the discharge heads also becomes greater than the ambient temperature.
However, the piezoelectric elements (e.g., piezoelements) that act as drive elements of the discharge heads have temperature characteristics, and the Vh displacement characteristics and the like fluctuate in accompaniment with temperature changes, and the discharge amount therefore fluctuates due to changes in the ambient temperature. The viscosity of the ink inside the discharge heads fluctuates in accordance with the temperature, and this also causes the discharge amount of fluctuate. Therefore, when the discharge heads move to the maintenance area in order to carry out maintenance after discharging (drawing) in the drawing area, the temperature of the discharge heads is reduced because the discharge heads are not producing heat and the heat of the control device is not present. When the discharge heads return to the drawing area and perform a discharge (drawing), variability occurs between initial discharges and later discharges.
Specifically, when the discharge heads move to the maintenance area to perform maintenance, the discharge heads stop producing heat and the temperature of the discharge heads is reduced when the driving of the drive elements of the discharge heads is stopped in the case, for example, that the nozzle surface is capped and a suction operation is carried out. Therefore, when the discharge heads are thereafter moved again to the drawing area and discharging (drawing) is immediately performed, discharge variability occurs as described above until the discharge heads having a lower temperature again warm up to an optimum temperature.
In view of the above, rather than immediately carrying out discharging (drawing) when the discharge heads have been moved again to the drawing area following maintenance, it is possible to consider waiting until the discharge heads warm up to the ambient temperature of the drawing area and then carry out a discharge (drawing) operation. However, in such a case, a new problem arises in that productivity is compromised because of the wait time.